Planar ferrite phase shifter for microwaves of increased bandwidth

ABSTRACT

A meander-like microstrip in a planar phase shifter is made of two parallel successions of straight strip sections. Each straight section has a length which is greater than the spacing between two sections. One end of each section in a succession is connected by a transverse strip section having an inclined position to the proximate opposite end of a section in the other succession.

United States Patent 1 [111 3,818,384 Schilz June 18, 1974 PLANAR FERRITE PHASE SHIFI'ER FOR [56] References Cited MICROWAVES OF INCREASED UNITED STATES PATENTS BANDWIDTH 3,753,162 8/1973 Charlton et al 333/24.1 [75] Inventor: Wolfram Schilz, Norderstedt,

Germany Primary Examiner-Paul L. Gensler [73] Assignee: U.S. Philips Corporation, New AUOMQX g 0r FirmFfank Trifilri York. NY.

[22] Filed: May 29, 1973 ABSTRACT V 1 App], 3 4,520 A meander-like microstrip in a planar phase shifter is made of two parallel successions of straight strip sections. Each straight section has a length which is [3 r g Appllcatlon Priority Data greater than the spacing between two sections. One June 22, 1972 Germany 2230390 end of each section in a succession is connected by a transverse strip section having an inclined position to [52] US. Cl. M the proximate opposite end of a ection i the other [51] Int. Cl. H0lp 1/32 succession [58] Field of Search 333/24.1, 24.2, 31 R 3 Claims, 3 Drawing Figures PATENTEDJUNI M 8.818.884

1'2 GHz 1'0 F Fig.3 A

PLANAR FERRITE PHASE SHIFIER FOR MICROWAVES OF INCREASED BANDWIDTH The invention relates to a planar ferrite phase shifter having a meander-like microstrip line.

Phase shifters of this kind which can be controlled continuously (analog phase shifters) or digitally are often used in the microwave technique. Particularly for the construction of phased aerial arrays, in which the bundled microwave beam is electrically deflected, a large number of phase shifters is required. Small dimensions and low losses are some of the essential aspects for the usability of the phase shifters in such systems.

Phase shifters of this kind are known inter alia from publications by G. E. Roome et al., I.E.E.E. Trans. MTT-16, 411 (1968), and G. R. Harrison et al., I.E- .E.E. Trans. M'IT-l9, 577 (1971). These phase shifters utilize as waveguides microstrip lines which are provided on ferrite substrates in the form of so-termed meander lines. Coupling of the fields of adjoining line segments results in the generation of a circularly polarized high-frequency field when a microwave is applied to the meander line, the said circularly polarized field being used for changing the phase shift. This effect is caused by the fact that the microwave is coupled, via this circular field, to the ferrite material which is used as the substrate, the said ferrite material being prepolarized by an adjustable static magnetic field. The effective permeability p. of the material is dependent on the strength of the static magnetization of the substrate and on the direction of this magnetization with respect to the propagation direction of the microwave.

By continuously changing the magnetization of, for example, a soft-magnetic ferrite material, a continuous phase shift (analog phase shifter) can be obtained; a discontinuous phase shift (latching phase shifter) can be obtained by switching over the remanent magnetization of hard-magnetic ferrites. In order to obtain the circular field, the width of the meander line is chosen to be such that the detour of the wave between two adjacent points amounts to one quarter wavelength 90. Because the meander line has filtering properties, there is an upper limit frequency f beyond which the attenuation of the line increases substantially.

At a given geometry of the meander line, the differential phase shift which can be obtained per unit of length, that is the phase shift between two switching states of the magnetization, is substantially dependent on the frequency. The differential phase shift increases particularly strongly in the region of the limit frequency f,,. This typical property of meander lines constitutes a critical limitation of the usable bandwidth and of the range of operating temperatures.

The invention has for its object to provide a phase shifter which has a constant differential phase shift over a large frequency range.

The phase shifter according to the invention is characterized in that the distance between adjacently arranged conductors is increased directly proportionally to the distance between the adjacently arranged meander lines in the direction of the closed end of each meander and is increased inversely proportionally to the width of the meander lines (fl-shaped structure). As a result, a substantial reduction of the frequencydependency of the differential phase shift is achieved. In the X-band, a substantially constant phase shift can be achieved in a comparatively large frequency range, (approximately 2 Gl-lz) by means of a ferrite substrate as well as by means of a non-magnetic substrate and ferrite blocks of a soft-magnetic or hard-magnetic material which are provided thereon.

The invention will be described in detail hereinafter with reference to the Figures.

FIG. 1 shows a known meandered phase shifter,

FIG. 2 shows an embodiment of a phase shifter according to the invention, and

FIG. 3 shows a graph in which the differential phase shift is plotted as a function of the frequency for the phase shifters shown in the FIGS. 1 and 2.

The known phase shifter which is shown in FIG. 1 comprises a substrate 1 which is provided with a meandered strip line 2 on its upper side, the line having a width w, a pitch s and the meanders having a width b. The substrate which is made, for example, of ferrite is provided on its lower side with a flat, properly conductive ground plane. As is known, a microwave applied to the phase shifter causes a field configuration in which the magnetic field lines are situated in planes prpendicular to the longitudinal direction of the conductors and circularly enclose the conductors. For each meander magnetic field lines of line segments which are adjacently arranged intersect each other. For each set of parallel line segments, one intersection can be observed below the plane of the strip line in the substrate for which the magnetic field lines intersect at right angles, the strength of the intersecting fields being equal, and these fields having been phase shifted with respect to each other. This means sthat a circularly polarized HF magnetic field appears in this intersection. A circularly polarized field of this kind appears for a given frequency, for example, halfway between the points I and II, the physical length between the points I and II, measured along the line 2, amounting to one quarter of the Wavelength. This known meandered phase shifter has a differential phase shift which is substantially frequecy-dependent, as appears from the upper graph given in FIG. 3 (denoted by this known meander structure).

From measurements performed on the meander line shown in FIG. 1 it was found that l. at a given width b of the meander line the phase shift per meander is substantially dependent on the distance s between two lines. Because the width w of the lines is determined by the impedance of the microstrip line, the quantity s/w can be considered as the decisive parameter. A reduction of s/w causes an increase of the phase shift per meander due to the fact that, when s/w is decreased, the parallel line segments of the meander will be situated nearer to each other, so that an increased field strength of the circularly polarized field is obtained.

2. The polarization state of the fields between the conductors can be characterized by the ellipticity e (if e i 1 the fields are circularly polarized; if e 0: the fields are linearly polarized). Measurements of the values of 6 along the line Ill-IV demonstrated that the point of circular polarization (6 l) is displaced with the frequency along the line III-IV.

These two effects are utilized as follows in the phase shifter according to the invention so as to achieve a compensation for the transmission characteristic of the meander line as a function of the frequency, and hence an increased bandwidth. In the phase shifter of this invention an increase of the frequency f causes an increase of the phase shift per meander. At the same time, the point of circular polarization (6 l) is displaced, the strongest coupling with the ferrite taking place in the direction IV. The frequency-dependent increase of the phase shift can be compensated for by a suitable extension of the structure, ie by increasing the parameter s/w. This results in the Q-shaped structure of the strip line 3 shown in FlG. 2, a linear increase of the distance between adjacently arranged line segments being used over a part it of the width b of the meander line. The difierential phase shift measured for this structure is shown in the lower graph of F IG, 3 (de noted by the Q-shaped meander structure) as a function of the frequency. As appears from this graph, this Q-shaped structure is utilized to produce a constant differential phase shift of approximately 40 over a frequency range of approximately 2 GHz between 9 GHz and 11 GHZ.

The use of polycrystalline YlG (yttrium -iron-gamet) (4 1r M 1800 Gauss) for the substrate is particularly advantageous. However, the substrate can alternatively be made of a non-magnetic material on which ferrite blocks of a soft-magnetic or hard-magnetic material are provided What is claimed is:

l. A planar phase shifter having a ferrite substrate adapted for being magnetically prepolarized and a conductive planar member on one side of the substrate, comprising a conductive strip on the opposite side of the substrate, said strip having a configuration formed of two substantially parallel rows of successively arranged straight strip sections, each straight section having a predetermined length and being spaced from a subsequent section in a row by a distance which is smaller than said length, and a plurality of shaped strip sections each connecting an end of a straight section in a row to the proximate opposite end of a straight sec tion in the other row.

2. A planar phase shifter according to claim 1 wherein each shaped strip section has straight end portions and an intermediate portion inclined relative to said straight end portions.

3. A planar phase shifter according to claim 2 wherein spacings between the straight sections in one row are located opposite central areas of respective straight sections in the other row.

y UNITED STATES PATENT OFFICE I I CERTIFICATE OF CORRECTION Patent No- 3.8l8.384 Dated June '18, 1974 In nt d s) WOLFRAM SCHILZ It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

on the title page, Section 30] change "2230390"'to signeci arad seal e ci" this 29th day of borobe z 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. Attesting Officer MARSHALL DANN Commissioner of Patents 

1. A planar phase shifter having a ferrite substrate adapted for being magnetically prepolarized and a conductive planar member on one side of the substrate, comprising a conductive strip on the opposite side of the substrate, said strip having a configuration formed of two substantially parallel rows of successively arranged straight strip sections, each straight section having a predetermined length and being spaced from a subsequent section in a row by a distance which is smaller than said length, and a plurality of shaped strip sections each connecting an end of a straight section in a row to the proximate opposite end of a straight section in the other row.
 2. A planar phase shifter according to claim 1 wherein each shaped strip section has straight end portions and an intermediate portion inclined relative to said straight end portions.
 3. A planar phase shifter according to claim 2 wherein spacings between the straight sections in one row are located opposite central areas of respective straight sections in the other row. 